Date: Wed, 19 Jan 2000 11:59:32 -0800 (PST) From: "Peter C. Wallace" <pcw@mesanet.com> To: freebsd-small <freebsd-small@FreeBSD.ORG> Subject: Re: PC/104 Message-ID: <Pine.BSF.4.20.0001191151240.5336-100000@freeby.mesanet.com> In-Reply-To: <Pine.LNX.4.05.10001190127570.11030-100000@jason.argos.org>
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On Wed, 19 Jan 2000, Mike Nowlin wrote: > > > One additional difference is that PC/104 supports IRQ sharing (across > > different devices on the bus). I don't remember the details <mumbles > > something about impedance and pull-up/down> > > I've been kinda wondering about this for a while.... From everything I've > been able to find, it's not the ISA bus itself that causes problems with > sharing IRQ's, but it's the cheap cards we're so used to seeing everywhere > that don't use open-collector drivers. I have successfully shared > interrupts using old (bulky, lots of chips, sucks up lots of power) cards > in the past, but the modern stuff hates it. > > Any input? > > mike Actuallly open collector does you no good because IBM in their great wisdom made the IRQ polarity active high (and edge triggered to boot). If you put a pull-down on the IRQ bus (contrary to standard practice) you can use an "open source" driver easily done in a PAL. We do this on some of our PC/104 cards but basically its M^2 logic... > > > > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-small" in the body of the message > Peter Wallace Mesa Electronics To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-small" in the body of the message
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